Characterisation of the dilator effects of acetylcholine (ACh; 10-5 M) in isolated pulmonary artery. Panel A shows an original recording from a typical experiment. After equilibration, vessels were contracted with U46619 (10-7 M), at plateau ACh was added and immediate dilation occurred. At plateau either L-NG-nitro-L-arginine methyl ester (L-NAME; 10-3 M) or apamin (5 × 10-7 M) plus charybdotoxin (10-7 M) was added. Finally where L-NAME had been added, apamin plus charybdotoxin were added and visa versa. Panels B and C show pooled data from several experiments where L-NAME or apamin plus charybdotoxin were added respectively. The data is expressed as the mean percentage of induced tone +/- the S.E.M and comprised of n = 4–6 experiments. A p-value of < 0.05 was taken as statistically significant, calculated by t-test and denoted by *.